Apparatus for duplicating long strips of film onto other strips of film is known. The use of this apparatus is common in the movie industry where the technique is used to make copies of movies for wide distribution. Other fields utilize apparatus for the same general purpose.
Electrophotographic film is advantageous because it need not be kept in darkness and usually is not as perishable as photographic film. Further, it can be developed quickly with less chemical steps and critical processes than required for photographic film. Commercially available electrophotographic coatings have disadvantages which have prevented their use in lieu of photographic film, and among these are:
1. They are not available in strip form capable of being handled in reels. PA1 2. They are slower than photographic film to a degree that requires a great deal of time to make duplicates of long strips. PA1 3. They have less resolution than photographic film. PA1 4. They cannot retain their charge and latent image if moved in contact with other surfaces such as those of photographic films. PA1 5. Static electricity generated as films separate destroys the latent image. PA1 6. They are not transparent.
In the copending application the same electrophotographic film is used to receive the duplicate images from photographic film but the films are not in contact, necessitating optical trains, slits, focussing, etc. The films move in directions opposite to one another. The films being spaced from one another, there are no problems of erasing the latent image from the surface of the electrophotographic film during transportation of the films through the apparatus, but the sharpness of the transfer and the accuracy thereof over a wide area are dependent upon the quality of the optical train. In the case of images whose dimensions must be accurately preserved, this poses difficulties which are solved, if at all, by expensive optical systems.
Contact printing is much more economical and results in higher quality. It was not known until the invention herein that contact printing of electrophotographic film could be effected without erasing the latent image since all known electrophotographic members have been incapable of having a latent image made thereon by direct contact with a conventional film negative. Some complex members have been evolved which have succeeded in obtaining contact transfer but these have not been commercially successful and do not have quality equivalent to photographic film. Further, they are quite expensive and necessitate the use of complex apparatus and are very slow.
The invention revolves around electrophotographic film which has none of these disadvantages and has many unique advantages which enable its use to receive and reproduce the projected images from electrophotographic film in a contact printer.
Once it has been imaged, conventional silver halide film is altered permanently and no longer can be used. This is because in developing the entire emulsion coating is changed permanently chemically. Electrophotographic coatings are not changed physically by imaging with electrostatic images that are latent and represent merely the distribution of electrical charges thereon. Accordingly, unless fixed by causing permanent adherence to electrophotographic film, developed images can be transferred or removed and the electrophotographic film reused.
Electrophotographic films as contemplated for use in the invention have characteristic colors which, while normally not objectionable, nevertheless are annoying when the film has been imaged and is to be used for projection. Accordingly, the invention utilizes the property of the electrophotographic film which enables transfer of the toned image to a clear base film, which also makes the electrophotographic film available for reuse.
Additional background is contained in said copending application and is incorporated herein by reference.